Acquiring a test subject's blood pressure information is extremely important in finding out the condition of the test subject's health. In recent years, attempts have been made to capture cardiac load, degree of arteriosclerosis and the like by acquiring the pulse wave of a test subject, rather than only by acquiring systolic blood pressure value (hereinafter, maximum blood pressure), diastolic blood pressure value (hereinafter, minimum blood pressure) and the like whose usefulness as typical indices for health management has been widely recognized heretofore. A blood pressure information measurement device is a device for obtaining these indices for health management based on acquired blood pressure information, and further utilization in areas such as early detection, prevention and treatment of circulatory system diseases is anticipated. Note that blood pressure information includes a wide variety of information on the circulatory system, such as various indices and the like indicating systolic blood pressure value, diastolic blood pressure value, mean blood pressure value, pulse wave, pulse, and degree of arteriosclerosis.
Generally, a cuff is used in the measurement of blood pressure information. Here, a cuff denotes a belt-like or annular structure that contains a fluid bag having an inner cavity, and can be wrapped around a part of the body, and refers to a device that is used in the measurement of blood pressure information by inflating and deflating the fluid bag through injecting a fluid such as a gas or a liquid into the inner cavity. Note that a cuff used by being wrapped around an arm in particular is also called an armband or a manchette.
Conventionally, as blood pressure information measurement devices configured to be capable of acquiring an index indicating the degree of arteriosclerosis, devices are known that utilize the fact that the transmission velocity of a pulse wave ejected by the heart (hereinafter, pulse wave velocity (PWV)) increases as arteriosclerosis advances, and acquire an index indicating the degree of arteriosclerosis based on the measured PWV.
One such known blood pressure information measurement device is configured so that a cuff and a sensor are fitted on two or more measurement sites selected from the four limbs, the neck and the like, pulse waves are acquired simultaneously with the fitted cuff and sensor, PWV is measured based on the appearance time lag of the acquired pulse waves and the artery length between the measurement sites, and an index indicating the degree of arteriosclerosis is acquired based on the measured PWV.
As for the PWV measured in the abovementioned blood pressure information measurement devices, brachial-ankle pulse wave velocity (baPWV) and carotid-femoral pulse wave velocity (cfPWV) are typical. baPWV is the PWV measured as a result of the upper arm and ankle being selected as measurement sites, and a device disclosed in JP 2000-316821A is an example of a blood pressure information measurement device configured to be capable of acquiring an index indicating the degree of arteriosclerosis based on baPWV. Also, cfPWV is the PWV measured as a result of the neck and thigh being selected as measurement sites.
However, with a blood pressure information measurement device such as described above that measures baPWV or cfPWV and acquires an index indicating the degree of arteriosclerosis based on the acquired PWV, because the PWV needs to be measured after fitting the cuff and sensor to a plurality of sites on the body, the device may become comparatively large and the device constitution may be comparatively complex. Thus, even if these blood pressure information measurement devices can be used in a medical facility or the like, the reality at present is that these devices cannot readily be used in the home.
Thus, a blood pressure information measurement device configured so as to measure PWV after cuffs have been fitted on different positions of the upper arm, and acquire an index indicating the degree of arteriosclerosis based on the measured PWV is disclosed in JP 2004-113593A, so as to enable the device to be configured compactly.
The blood pressure information measurement device disclosed in JP 2004-113593A is configured such that cuffs are fitted to different positions on the upper arm, with an air bladder for occlusion contained in the cuff fitted on the distal side and an air bladder for pulse wave measurement contained in the cuff fitted on the proximal side, and a pulse wave is detected using the air bladder for pulse wave measurement in the state where the artery is occluded using the air bladder for occlusion, PWV is measured based on the time lag at which the peak value of an ejection wave component and the peak value of a reflective wave component included in the detected pulse wave appear and the artery length between the different positions of the upper arm on which the cuffs are fitted, and an index indicating the degree of arteriosclerosis based on the measured PWV is acquired. Here, an ejection wave is the pulse wave transmitted from the proximal side to the portion of the artery on which the air bladder for pulse wave measurement is fitted, and a reflective wave is the pulse wave transmitted from the distal side to the portion of the artery on which the air bladder for pulse wave measurement is fitted as a result of the ejection wave being reflected at the portion on which the air bladder for occlusion is fitted.
However, because two cuffs still need to be fitted even with the blood pressure information measurement device disclosed in the abovementioned JP 2004-113593A, it cannot be said that sufficient miniaturization has been achieved, and further miniaturization is needed to use the device in the home.
In view of this, a blood pressure information measurement device configured so as to measure PWV after a single cuff has been fitted on the upper arm, and to acquire an index indicating the degree of arteriosclerosis based on the measured PWV is disclosed in JP 2007-044362A, so as to enable the device to also be used in the home.
The blood pressure information measurement device disclosed in JP 2007-044362A is configured such that one large-volume air bladder for blood pressure value measurement and two small-volume air bladders for pulse wave measurement are contained in a cuff that is wrapped around the upper arm, and in the fitted state, one of the air bladders for pulse wave measurement is disposed on the proximal side of the air bladder for blood pressure value measurement and the other air bladder for pulse wave measurement is disposed on the distal side of the air bladder for blood pressure value measurement, blood pressure values are measured using the air bladder for blood pressure value measurement, and PWV is measured based on the appearance time lag of the pulse waves detected using the two air bladders for pulse wave measurement and the distance between these two air bladders for pulse wave measurement, and an index indicating the degree of arteriosclerosis is acquired based on the measured PWV.
However, with the blood pressure information measurement device disclosed in the abovementioned JP 2007-044362A, because the device is configured to detect the pulse wave using the two air bladders for pulse wave measurement without occluding the artery included at the fitting site of the cuff, the reflective wave from the artery positioned on the distal side of the fitting site will be superimposed on the pulse wave that is detected, making it difficult to appropriately separate the reflective wave, and resulting in a significant drop in PWV measurement accuracy. Thus, in the case where the blood pressure information measurement device is configured as disclosed in JP 2007-044362A, it is difficult to raise the accuracy of the index indicating the degree of arteriosclerosis that is acquired.
Blood pressure information measurement devices that have achieved device miniaturization to an extent that enables use in the home, and can, moreover, measure PWV with high accuracy, enabling an index indicating the degree of arteriosclerosis to be acquired with high accuracy as a result, are disclosed in JP 2009-284965A and JP 2009-284966A, for example.
The blood pressure information measurement devices disclosed in JP 2009-284965A and JP 2009-284966A are configured such that a single cuff is fitted on the upper arm, with one large-volume air bladder for blood pressure value measurement and one small-volume air bladder for pulse wave measurement contained in the cuff, and in the fitted state, the air bladder for pulse wave measurement is disposed on the proximal side of a fitting site, while the air bladder for blood pressure value measurement is disposed on the distal side of a fitting site, blood pressure values are measured with the air bladder for blood pressure value measurement, and a pulse wave is detected using the air bladder for pulse wave measurement while maintaining a state in which the artery is occluded using the air bladder for blood pressure value measurement, and PWV is measured based on the time lag at which the peak value of an ejection wave component and the peak value of a reflective wave component included in the detected pulse wave appear and the artery length from the heart (more specifically, subclavian artery bifurcation) to the iliac artery bifurcation, and an index indicating the degree of arteriosclerosis is acquired based on the measured PWV. Here, an ejection wave is the pulse wave that is transmitted directly from the heart to the portion of the artery on which the air bladder for pulse wave measurement is fitted, and a reflective wave is the pulse wave transmitted to the portion of the artery on which the air bladder for pulse wave measurement is fitted as a result of the ejection wave being reflected at the iliac artery bifurcation.
With the blood pressure information measurement devices disclosed in JP 2009-284965A and JP 2009-284966A, because a configuration is employed in which a single cuff is fitted on the upper arm, and one air bladder for blood pressure value measurement and one air bladder for pulse wave measurement are contained in a single cuff, and because the device can be miniaturized as compared with conventional technology, and the air bladder for blood pressure value measurement can also be used as a cuff for occluding an artery, pulse wave measurement can be performed in a state in which the distal side is occluded, enabling PWV to be measured with high accuracy, without the possibility of the reflective wave from an artery positioned on the distal side of the fitting site being superimposed on the pulse wave that is detected. The blood pressure information measurement devices disclosed in JP 2009-284965A and JP 2009-284966A can also be configured to inflate the air bladder for blood pressure value measurement and the air bladder for pulse wave measurement simultaneously or selectively using a single inflation pump, in which case, further miniaturization of the device and simplification of the device configuration will also be achieved.
Accordingly, if a blood pressure information measurement device as disclosed in JP 2009-284965A and JP 2009-284966A is employed, miniaturization of the device and simplification of the device configuration to an extent that enables use in the home is achieved, and, moreover, PWV can be measured with high accuracy, enabling an index indicating the degree of arteriosclerosis to be acquired with high accuracy as a result.
Note that JP 2009-284965A and JP 2009-284966A also describe being able to acquire an index indicating the degree of arteriosclerosis based on the difference, ratio or the like of an amplitude of the ejection wave component and an amplitude of the reflective wave component included in the detected pulse wave, besides the abovementioned acquisition of an index indicating the degree of arteriosclerosis based on PWV.
Also, in addition to JP 2009-284965A and JP 2009-284966A, JP 2004-195071A and JP 2007-522857A describe applying a higher compression force than maximum blood pressure to an artery when detecting a pulse wave, and performing various types of pulse wave analysis based on the pulse wave detected in that state, given that differences arise in the shape of the pulse waves detected in the case where the compression force at the time of compressing an artery differs.    Patent Literature 1 JP 2000-316821A    Patent Literature 2 JP 2004-113593A    Patent Literature 3 JP 2007-044362A    Patent Literature 4 JP 2009-284965A    Patent Literature 5 JP 2009-284966A    Patent Literature 6 JP 2004-195071A    Patent Literature 7 JP 2007-522857A